Spotted seahorse

The common seahorse (Hippocampus kuda) is a strange hodgepodge of characters, from the top of its equine head to the tip of its prehensile tail. But its unusual appearance is as nothing compared with its unique approach to breeding: famously, in seahorses, pipefishes and sea dragons it is the male of the species that carries the pregnancy.

The female uses her ovipositor to inject eggs into a pouch on the male's belly, where they are fertilised and grow into tiny replicas of adults over the course of three to four weeks.

Twin-spot lionfish

Found across the Indo-Pacific and in Australia's coastal waters, the twin-spot lionfish (Dendrochirus biocellatus) is a secretive – if aggressive – fish that is usually seen only at night.

It is also known as the Fu Manchu lionfish for the two tentacle-like protrusions above its mouth that look vaguely moustache-like.

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Olive ridley sea turtle

One of just seven species of sea turtle, the olive ridley (Lepidochelys olivacea) is found in the Pacific and Indian oceans, and in the south Atlantic. It nests on only a handful of beaches around the world, arriving in large numbers in spectacular mass nesting events known as arribadas.

Blue blubber jellyfish

Although labelled the blue blubber, this jellyfish (Castostylus mosaicus) can come in a number of colours from white to purple. It has a very unusual feeding system for a jellyfish. Buried within the cells of its body are thousands of symbiotic algae; they photosynthesise, providing nutrients and energy for the jellyfish host.

The blue blubber is native to waters of Australia. Overfishing has removed many of its natural predators, resulting in a huge rise in numbers. That's good news for some, though: the jellyfish is considered a delicacy in Japan and China.

North Pacific giant octopus

True to its name, the North Pacific giant octopus (Enteroctopus dolfeini) is the largest of all octopus species.

Like other octopuses, they stand head and multiple shoulders above other invertebrates in terms of intelligence. The North Pacific giant, however, grows to 45 kilograms and typically measures around 4 metres from arm tip to tip. Yet they live for just five years at most.

As the common name suggests, this octopus is found in the North Pacific Ocean, along the continental shelf from the Aleutian Islands west of Alaska to Baja California in Mexico and north-eastern Japan.

They feed on bivalves, crabs and lobsters. When it has finished its meal, the octopus pushes the remains out of its den's opening, creating an "octopus garden", or midden, of empty shells.

Males compete for the attention of females by building nests that the females can use to house their eggs. The male then takes on the role of house-husband, guarding the nest from predators while feeding on diseased eggs that could threaten the rest.